A few years back, a post on this blog looked at examples of PHP design patterns that had missing parts. In 2006, an IBM sponsored post introduced PHPers to design patterns in “Five common PHP design patterns.” This was an important post because it demonstrated that far from being the exclusive domain of languages like Java, design patterns were applicable to PHP as well. However, of the five patterns, (Factory [Factory Method], Singleton, Chain-of-Command [Chain-of-Responsibility] , Observer, and Strategy) two (Factory and Chain-of-Command) were misnamed and misrepresented, one (Singleton) has since been more-or-less deprecated as a pattern (by no less than Erich Gamma) and the other two were iffy in their implementation.

Like lemmings following each other over a cliff, PHPers often followed each wrong example, further perpetuating the ill-formed pattern. So, when we look at patterns, lest PHP programmers be considered rank amateurs, we need to get patterns right. One of the most common mistakes with the Strategy pattern is either ignoring or leaving out the Context class altogether. In Part I of this two-part series, we saw what a Near-Strategy pattern looks like without a Context class. In Figure 1 of that same post, you can see the class diagrams of the Near-Strategy and Strategy patterns. The example in this post is of a correctly formed Strategy pattern. Play the Strategy example and Download the files with the following two buttons:

The Context Participant

To get the Context right, we need to go to the original source, Design Patterns: Elements of Reusable Object-Oriented Software. The Context participant has the following characteristics:

Configured with a ConcreteStrategy object

Maintains to reference to a Strategy object

May define an interface that lets Strategy access its data

At the heart of the Strategy design pattern, the Context and Strategy interact to implement the selected algorithm in the form of a concrete strategy. The key here is,

The Strategy lets the algorithm vary independly from clients that use it.

In order to do this,

A context forwards requests from its clients to its strategy. Clients usually create and pass a ConcreteStrategy object to the context; thereafter, clients interact with the context exclusively.

Figure 1 shows the path used in this implementation:

Figure 1: The path through the context to request an algorithm (concrete strategy)

The path begins with the Client creating an instance of a specific concrete strategy (received from the HTML UI) and using that instance as a parameter to make the request through the context. From this point on, the client no longer is in contact with the strategy but instead the context. The context takes the instance passed from the client and makes the request through the strategy interface [algorithmInterface()]. Any client can make similar requests through the context by passing the concrete strategy through its context interface. That can be very handy when your program has more than a single client requiring a strategy.Continue reading ‘PHP Strategy Design Pattern Part II: Add a Context’

Design Patterns are general OOP solutions for any computer language, and yet each language has different typical uses. One of the most important uses of PHP is to communicate with MySql. As the “middleman” between HTML and MySql, developers need to juggle three languages well in the HTML< ->PHP< ->MySql sequence and shuffle. All of the OOP work, though, belongs to PHP since neither HTML nor MySql is object oriented. This post is dedicated to the fundamental OOP questions surrounding HTML< ->PHP connections, instantiating class instances and creating re-usable MySql classes. I’d also like to touch on using comments in code and perhaps stir up a little controversy with comments about certain “standards” for comments in PHP.

The first thing to do is to take the program for test drive and look at the code. Run the program by clicking the Play button and click the Download button to get the files.

The HTML Communication

Object oriented programming is all about objects communicating with one another. The first communication is between HTML and the PHP object it first calls. As the user interface (UI), the HTML document must get data from the user and pass it to PHP for processing. In PHP object communication, each object can call the object as a whole or specify a method or property in the other object to perform a specific task. With HTML, we pretty much have to be satisfied with a call to an object (or object trigger) and depend on PHP to carry the ball from that point on. However, if an HTML document has several forms, each form can call a different object, or each form submit button can have a different name. By using the unique name for each submit button a single Client class can determine which operation the user requests. The following HTML is set up for that purpose:

One thing that may stir the pot (among developers) found in the HTML document is the use of iframe tags. HTML5 retained iframes, and in the jQuery Mobile documentation, you will find the use of iframes. They no longer present a hazard to SEOs; and so I don’t see the harm using them to display PHP output. Besides, I could not find a suitable replacement. (I’m not about to mix PHP and HTML to create a workable hack straight out of the 9th circle of Hell.) So see if you can live with iframes for now, and we’ll get smelling salts for the fainters.

The Client Sorts it Out

When the UI has many options that must be handled by a client object to make the appropriate request from a collection of objects, each with a single responsibility, there’s going to be some kind of conditional statement to sort out which object to use. For lots of good reasons that I won’t go into here, switch/case and if/ifelse statements are to be used sparingly and judiciously in OOP and design pattern programming. An alternative approach would be to add several methods to the Client class and then have individual trigger files launched from the different forms in the HTML document call the appropriate Client method. That’s messy, but because HTML cannot address a class method, that may actually be a more orthodox approach. (Keep those smelling salts handy.)

The basic logic of the approach used is this:

When a submit button is pressed it can be trapped by the isset() method

Provide a name for each submit button

Test for variable being set and not NULL

Once tested use unset() to remove set state

Call object of set variable

Now take a look at the Client class to see how that reasoning has been implemented:

That’s all there is to the communication between HTML and the PHP Client class. The Client works (as do all client classes) to make requests. The origin of the request is the user through the HTML UI.Continue reading ‘Basic PHP-MySql OOP’